1. Field of the Invention
The present invention relates to a system for performing an operation relating to a printed wiring board (PWB) and particularly to the art of supporting a PWB. A PWB with electric components (e.g., electronic components) being mounted thereon should be called as a printed circuit board (PCB) but, in the present specification, a PCB is also referred to as a PWB, for avoiding complexity.
2. Discussion of Related Art
Generally, a PWB includes a thin substrate formed of an electrically insulating material such as a synthetic resin, and a circuit pattern formed of an electrically conductive material on the thin substrate. Thus, the PWB has flexibility. Therefore, when electric components (ECs) are mounted on the PWB, or when an adhesive or a creamed solder is applied to the PWB before the mounting of ECs, the PWB cannot maintain an accurate planeness or flatness, unless a back surface of the PWB is supported at a considerably large number of points.
To solve this problem, Japanese Patent Document No. 7-15189 teaches using supporting pins to support a back surface of a PWB. More specifically described, this document discloses a PWB supporting device including a base plate and a plurality of supporting pins. Each of the supporting pins has, at one of lengthwise opposite ends thereof, a support surface to support a PWB, and the other end portion of the each pin is formed of a permanent magnet. Thus, each supporting pin can be fixed owing to a magnetic force to the base plate that is formed of a magnetic material.
The supporting pins support the back surface of the PWB. However, the supporting pins must not engage uneven portions of the PWB itself or the ECs already mounted on the back surface thereof. Therefore, the supporting pins must engage only limited portions of the back surface of the PWB. Generally, different sorts of PWB have different patterns of limited portions that can be engaged by the supporting pins. Therefore, when the current sort of PWBs for each of which an operation is to be performed are changed to a new sort of PWBs, the supporting pins are re-arranged on the base plate. In the case where the supporting pins are automatically re-arranged, a force that can overcome the magnetic force being exerted on each supporting pin is applied to the each pin in a direction away from the base plate, so as to detach the each pin from the base plate. Subsequently, supporting pins that are to support the new sort of PWBs are attached to the base plate.
When each supporting pin is detached from the base plate, the each pin, however, is not detached before the force applied to the each pin overcomes the magnetic force. Once the force applied to the each pin overcomes the magnetic force, the magnetic force abruptly decreases as the each pin is moved away from the base plate. Thus, an impact occurs to the base plate, so that the base plate is vibrated and an impact sound is produced. If a smaller magnetic force is exerted to the each pin, a smaller impact will occur. However, the smaller magnetic force may be too weak to fix the each pin to the base plate.
The present invention provides a PWB-relating-operation performing system that has each feature described below. The following features are described, like claims, in respective paragraphs that are given respective sequential numbers. Any feature that includes another feature shall do so by referring to the number given to the latter feature. However, the following features and the appropriate combinations thereof are just examples to which the technical features, and the combinations thereof, described in the specification are by no means limited. In addition, in the case where one feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed in the one feature. That is, it is possible to select and employ only a portion (one, two, . . . , but not all) of those items.
(1) According to a first feature of the present invention, there is provided a system for performing an operation relating a printed wiring board, comprising a first supporting table which has a planar first supporting surface, at least a portion of the first supporting table that defines the first supporting surface being formed of a ferromagnetic material; a plurality of supporting members each of which has a seat portion having a bottom surface which is seated on the first supporting surface, and a support surface which is opposite to the bottom surface, at least a portion of the seat portion being formed of a permanent magnet, the each supporting member being attached, owing to a magnetic force of the permanent magnet, to the first supporting surface to support a back surface of the printed wiring board; an operation performing device which performs an operation for a front surface of the printed wiring board whose back surface is supported by the respective support surfaces of the supporting members; a second supporting table which is provided in a vicinity of the first supporting table and has a second supporting surface which is substantially continuous with the first supporting surface on a common plane, at least a portion of the second supporting table that defines the second supporting surface being formed of a ferromagnetic material; and a supporting-member moving device which moves the each supporting member from the second supporting surface to the first supporting surface, and from the first supporting surface to the second supporting surface, by sliding the each supporting member on the first and second supporting surfaces.
Each of the supporting members may be either a holding member, recited in the fifth feature (5), that supports the printed wiring board (PWB) while applying negative pressure to the board and thereby holding the same, or a simple member which just supports the PWB and does not have the holding function.
The operation performing device may be an electric-component mounting device which mounts electric components (ECs) on a front surface of PWB; a screen printing machine which screen-prints creamed solder on a front surface of a PWB; a highly-viscous-fluid applying device which sequentially applies a highly viscous fluid, such as adhesive, to a single spot, or plural spots, on a front surface of each of PWBs; or an electric-circuit inspecting device which inspects an electric circuit formed on a front surface of a PWB.
The first and second supporting surfaces may be always kept substantially continuous with each other on the common plane, or may be temporarily made substantially continuous with each other on the common plane. In the former case, the first and second supporting surfaces may be provided by a single continuous planar surface, or two planar surfaces which are independent of each other and are contiguous with each other without a gap or a step therebetween or adjacent to each other with a small gap or step therebetween. The phrase xe2x80x9csubstantially continuousxe2x80x9d used in this feature means that the first and second supporting surfaces do not have a gap or step therebetween, or have such gap and/or step which allow each supporting member to slide and move between the two supporting surfaces. More specifically described, the first and second supporting surfaces may have a step having such a dimension which assures that, owing to a roundness or a chamfer which is present at an edge of the bottom surface or the support surface of each supporting member and has the function of guiding the each supporting member, the each supporting member can be moved over the step; and/or a gap having such a dimension which is sufficiently smaller than that of the bottom surface of each supporting member and assures that in a state in which one of the first and second supporting surfaces is stably supporting the bottom surface of the each supporting member, the other supporting surface starts supporting a portion of the bottom surface. In the case where the first and second supporting surfaces are temporarily made substantially continuous with each other, at least one of the first and second supporting surfaces is moved relative to the other supporting surface in at least one of a direction parallel to, and a direction perpendicular to, the supporting surfaces. When each supporting member is moved between the first and second supporting surfaces, those supporting surfaces are made substantially continuous with each other on the common plane.
The common plane on which the first and second supporting surfaces are substantially continuous with each other may be either a horizontal plane or a plane inclined relative to the horizontal plane. In the case where the first and second supporting surfaces are temporarily made substantially continuous with each other, it is not essentially required, in a state in which the two supporting surfaces are not continuous with each other, that the two supporting surfaces are parallel to each other.
One of the first and second supporting tables may be provided by a PWB supporting device which supports the PWB for which the operation is performed; and the other supporting table may be provided by a supporting-member storing device in which the supporting members attachable to the first supporting table are stored. The first and second supporting tables may be alternately provided by the PWB supporting device and the supporting-member storing device. For example, the PWB-relating-operation performing system may comprise an EC mounting system which mounts ECs on a PWB, the operation performing device may comprise an EC mounting device which takes ECs from an EC supplying device and mounts the ECs on the PWB supported by the PWB supporting device, and the EC supplying device may comprise a table and a plurality of feeders placed on the table such that respective EC-supply portions of the feeders are arranged in a direction parallel to the PWB-convey direction. In this case, it is possible to employ two PWB supporting devices for a first mounting area and a second mounting area, respectively, which correspond to a first group of feeders, and a second group of feeders, of the EC supplying device, divided from each other at the middle position as seen in the above-direction direction. The EC mounting device mounts ECs, alternately on respective PWBs supported by the two PWB supporting devices. In this case, one of the two PWB supporting devices that currently supports the PWB on which ECs are not being mounted by the EC mounting device, functions as the supporting-member storing device. The table of the EC supplying device can support a sufficiently large number of sorts of feeders that assure that the EC mounting device can mount ECs on a plurality of sorts of PWBs. More specifically described, a first portion of the table that corresponds to the first mounting area supports such feeders that feed ECs to only such sorts of PWBs conveyed to the first mounting area only, and such feeders that frequently feed ECs to those sorts of PWBs; and the second half portion of the table that corresponds to the second mounting area supports such feeders that feed ECs to only such sorts of PWBs conveyed to the second mounting area only, and such feeders that frequently feed ECs to the latter sorts of PWBs. Therefore, each of the feeders is near to a PWB supported by a corresponding one of the PWB supporting devices, and the EC mounting head has only to move short distances to mount ECs on each PWB. This leads to improving the efficiency of mounting of ECs. However, it is possible to employ feeders which feed ECs to both respective PWBs supported by the PWB supporting devices in the first and second mounting areas. In this case, those feeders are placed on a middle portion of the table as seen in the above-indicated direction.
Each of the supporting members is attached, owing to a magnetic force, to each of the first and second supporting tables. The bottom surface of each supporting member and the first and second supporting surfaces are all planar or flat surfaces. Therefore, when the supporting-member moving device applies a force to each supporting member in a direction parallel to the first and second supporting surfaces, each supporting member is moved relative to the supporting surfaces, i.e., slid on the same. At this time, each supporting member receives a force equal to the product of the magnetic force and a friction coefficient with respect to the bottom surface of each supporting member and the first or second supporting member, in a direction to resist the movement of each supporting member. When this resistance force is overcome by the force applied by the supporting-member moving device to each supporting member, the each supporting member starts moving. This resistance force is small, and each supporting member can be moved with a smaller force than a force which is applied to the each supporting member in a direction parallel to the axis line thereof and away from the first or second supporting surface in order that the each supporting member may be detached from the supporting surface. Since a kinetic friction coefficient is smaller than a static friction coefficient, some impact is produced when each supporting member starts moving. However, this impact is smaller than that produced when each supporting member is detached from the first or second supporting surface. Therefore, a great magnetic force may be employed to sufficiently strongly attach each supporting member to the first or second supporting table, on one hand, and a small force may be applied by the supporting-member moving device to the each supporting member to move the same, on the other hand. In addition, only small vibration or noise is produced by the first and second supporting tables and the supporting-member moving device.
(2) According to a second feature of the present invention that includes the first feature (1), the operation performing system further comprises a printed-wiring-board conveying device which carries in the printed wiring board to a position aligned with the first supporting table, and carries out the printed wiring board from the position.
At the position aligned with the first supporting table, the operation is performed for the front surface of the PWB whose back surface is supported by the supporting members attached to the first supporting table.
(3) According to a third feature of the present invention that includes the second feature (2), the printed-wiring-board conveying device comprises two guide rails whose distance is changeable; a printed-wiring-board moving device which moves the printed wiring board along the guide rails; and a width changing device which changes the distance of the two guide rails and thereby changes a width of conveying of the printed wiring board.
When the distance of the two guide rails is changed, both of the two guide rails may be moved relative to each other, or one of the two guide rails may be moved relative to the other guide rail.
Each supporting member can be moved by a force which is applied thereto in a direction perpendicular to the axis line thereof. Therefore, if at least one of the guide rails is moved and may collide with the supporting members attached to the first supporting surface of the first supporting table, the supporting members falls to the first supporting surface, allowing the guide rail or rails to be moved. Thus, the supporting members and the rails are prevented from being damaged.
(4) According to a fourth feature of the present invention that includes the third feature (3), the second supporting table is provided at a position aligned with a space remaining between the two guide rails when the distance of the two guide rails is shortest, and the second supporting surface has a width not longer than the shortest distance.
According to this feature, the guide rails do not interfere with the supporting members attached to the second supporting table, even if one or both of the guide rails may be moved. Therefore, the second supporting table can function as a storing device in which the supporting members detached from the first supporting table are stored. Since the guide rails cannot interfere with the supporting members attached to the second supporting table, it is not needed to employ any measures to prevent each supporting member from being damaged if the each supporting member would be interfered with by the guide rails and fall down to the second supporting surface. Therefore, on the second supporting table, the supporting members may be arranged at a short pitch, i.e., at a high rate.
(5) According to a fifth feature of the present invention that includes any one of the first to fourth features (1) to (4), the first holding table comprises a holding table having a holding surface as the first supporting surface, and a plurality of negative-pressure-supply holes opening in the holding surface, and the supporting members comprise a plurality of holding members each of which has a negative-pressure passage formed therethrough, and is set on the holding surface of the holding table such that the negative-pressure passage thereof is communicated with at least one of the negative-pressure-supply holes, so that the support surface of the each holding member supports the back surface of the printed wiring board and a negative pressure supplied via the negative-pressure passage from the at least one negative-pressure-supply hole is applied to the back surface of the board to hold the board.
Since the holding members apply negative pressure to the PWB and thereby attract the same to the respective support surfaces thereof, the PWB is corrected to be plane even if it may have an upwardly convex warpage.
The holding members can be engaged with only limited areas of the back surface of the PWB. Therefore, the holding members are not attached to all of the negative-pressure-supply holes. Thus, it is needed to prevent the leakage of negative pressure from the negative-pressure-supply holes to which the holding members are not connected. The leakage of negative pressure may be prevented by, e.g., closing, with the closing members recited in the sixth feature (6) described below, the negative-pressure-supply holes, or alternatively, as will be described in DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS, providing the negative-pressure-supply holes with respective opening and closing valves which are opened when the holding members are connected to the corresponding supply holes to communicate the respective negative-pressure passages of the holding members with the corresponding supply holes but remain closed in a state in which the holding members are not connected to the supply holes.
(6) According to a sixth feature of the present invention that includes the fifth feature (5), the operation performing system further comprises a plurality of closing members each of which has a bottom surface which is seated on the holding surface of the holding table, at least a portion of the each closing member that is located in a vicinity of the bottom surface being formed of a permanent magnet, the each closing member being attached, owing to a magnetic force of the permanent magnet, to the holding surface to close one of the negative-pressure-supply holes that is not communicated with the negative-pressure passages of any holding members; a third supporting table which is provided in a vicinity of the holding table and has a third supporting surface which is substantially continuous with the holding surface on the common plane, at least a portion of the third supporting table that defines the third supporting surface being formed of a ferromagnetic material; and a closing-member moving device which moves the each closing member from the third supporting surface to the holding surface and from the holding surface to the third supporting surface, by sliding the each closing member on the third supporting surface and the holding surface.
The above description of the relationship between the first and second supporting surfaces applies to that between the first supporting surface as the holding surface, and the third supporting surface.
Like each supporting member, each closing member can be moved or slid on the third supporting surface and the holding surface, by a force applied thereto in a direction parallel to those surfaces. Therefore, the closing-member moving device can move, with a small force, each closing member which is attracted, by a great magnetic force, to the third supporting table or the holding table. When each closing member is moved, only small vibration, impact, and noise are produced.
(7) According to a seventh feature of the present invention that includes the sixth feature (6), the third supporting table is provided by the second supporting table, and the closing members are supported on the second supporting surface.
(8) According to an eighth feature of the present invention that includes the sixth or seventh feature (6) or (7), the closing-member moving device is provided by the supporting-member moving device.
(9) According to a ninth feature of the present invention that includes any one of the first to eighth features (1) to (8), the operation performing device comprises an operation performing head, and the supporting-member moving device moves the operation performing head in a direction parallel to the first supporting surface.
When the operation performing head performs the operation, the supporting-member moving device moves the operation performing head relative to the PWB. Thus, the present operation performing system can enjoy a simple construction.
(10) According to a tenth feature of the present invention that includes any one of the first to ninth features (1) to (9), the supporting-member moving device comprises at least one engageable portion which is engageable with a portion of the each supporting member that is near to the bottom surface thereof.
(11) According to an eleventh feature of the present invention that includes any one of the first to tenth features (1) to (10), the supporting-member moving device comprises a pair of grasping members which are engageable with the each supporting member.
(12) According to a twelfth feature of the present invention that includes any one of the first to eleventh features (1) to (11), the supporting-member moving device comprises a holding device which holds the each supporting member; and a rotating device which rotates said each supporting member held by the holding device.